Study On The Characteristic Of Cavitation Erosion In Hydraulic Pump And Valve

With the development of science and technology, hydraulic technology has become a foundational technology, including transmission, control and detection technology. It has been increasingly influencing advanced machinery equipment significantly. Recently, hydraulic technology is connecting micro-electronics technology and high power controlled object inseparably. Thus, it has been indispensable link and means in the modern control engineering.Currently, hydraulic technology is developed along the dominant directions: high pressure, high speed, high power, low noise, high reliability and high integration, and having obtained significant development. However, in high pressure hydraulic systems, cavitation appears easily. Because cavitation produces air bubbles inevitably, if the structure of hydraulic component can not be designed properly, the air bubbles will be gathered near the solid surface of hydraulic component, or even collapse. The collapsing of air bubble near solid surface causes cavitation erosion damage on hydraulic component, and serious cavitation noise appears simultaneously. In hydraulic system, cavitation damage is very serious and complicated, so that simple technology and methods are needed to estimate the cavitation erosion and cavitation noise characteristic of hydraulic component accurately and rapidly under the existing condition in the practical project.Focusing on the problems above, this study takes the advantages of CFD analysis, noise test, flow visualization, and the theory analysis on cavitation noise. The cavitation characteristic of axial plunger pump and hydraulic control valve are studied deeply and systematically, both of which are key components in high pressure and high power hydraulic system. The method to estimate cavitation characteristic by analyzing impingement angle at the groove on porting plate of an axial plunger pump is put forward during design process period. Otherwise, as hydraulic control valves are concerned, a method is proposed to estimate cavitation noise characteristic based on the distributions of pressure and velocity direction on valve seat, and along the stream direction.The main contents of this paper are as follows: 1) The cavitation erosion principle of hydraulic component in high pressure system is analyzed based on the theories of cavitation and cavitation erosion. From the view point of sound source and dissemination, it is put forward that if cavitation bubble collapses far away from solid wall, the vibration will be attenuated by fluid, and then noise is small. Conversely, if cavitation bubble collapses nearby or on the solid wall of hydraulic component, the vibration will not be attenuated, but be enlarged by solid and disseminate in the air, thus the cavitation noise will be very large. It can be obtained that, regardless of viewpoint on controlling cavitation erosion or cavitation noise in hydraulic system, the collapse position of cavitation bubble should be set far away from the solid wall by changing the structure of hydraulic component.2) CFD knowledge is introduced as the theory basic of modeling and calculation, and then computational models of several hydraulic components have been established based on it. Firstly, being concerned of the compressibility of hydraulic oil, the 3D transient model of axial plunger pump is made for analyzing the porting progress of it with the technology of moving mesh. Secondly, the 2D steady models of two types of poppet valves and two types of non-full-circular opening spool valves are also made.3) The cavitation erosion characteristic of high pressure hydraulic plunger pump is studied by CFD calculation and experiment. Based on them, the reasons of cavitation erosion on surface of porting plate and pump chamber are analyzed, linking the principle of impingement with the theory of bubble collapse. Then, the method to estimate cavitation erosion characteristic of high pressure piston plunger pump by analyzing impingement angle on outlet of throttling groove is put forward. That is, to hold the impingement angle range of 30°～60°as appraisal criterion of cavitation erosion characteristic on high pressure hydraulic plunger pump.4) The throttling characteristic of hydraulic control valve is studied by CFD calculation and experiment. Combining the principle of sound dissemination with bubble collapsing, noise mechanism of hydraulic control valve is analyzed. Considering the noise characteristic curves obtained by experiment and CFD solution, the distributions of pressure and velocity direction on valve seat along the stream direction are analyzed by weighted integral method. A noise characteristic estimate index C_N is proposed based on pressure distribution and backflow of vortex shedding.